Add a message to the dialog when the user is about to download the AR module with a metered network.
Add a message to the dialog when the user is about to download the AR module with a metered network.

That AR mode is for an on-site experience.

Bug: 128656798
Change-Id: I8dbad4ac6a906480c827f93bcd697ee314bae032

google/iosched,google/iosched,google/iosched